As far as gameplay is concerned, we need to create continents and fill them. I would opt for one small continent to start with. Once a continent and some basic features (a mountain range somewhere, the largest river, etc.) are established, everyone can go and work on his or her favorite area and flesh it out.
So the 2nd chapter of the Creation story would be something like "XXX saw that the world was empty, so he decided to raise a piece of land from the depth. It was in the shape of a hat and a thousand miles across. He named it ABC."